The invention relates to a fuel cap adsorbing vaporized fuel vaporized from a fuel contained in a fuel tank and preventing leakage of the vaporized fuel to the air, and a vaporized fuel adsorption canister used in the fuel cap.
An internal combustion engine of a relevant vehicle employs a vaporized fuel adsorption canister to adsorb a generated vaporized fuel so as to prevent leakage of the vaporized fuel to the air. It is necessary for a small utility engine or a two-wheeled vehicle to prevent leakage of the vaporized fuel vaporized from the fuel contained in a fuel tank to the air while suppressing an increase in internal pressure. In this respect, Japanese Patent Application Laid-Open No. 7-34985 discloses a technique for providing a vaporized fuel adsorbing device within a fuel cap that opens or closes a fuel filler port provided at a fuel tank of a small utility engine. The fuel cap using the disclosed technique has been gradually considered.
The fuel cap of this type includes an outer cap serving as an outer envelope and an inner cap fitted into the outer cap. The inner cap is inserted in the fuel filler port and the fuel filler port is closed by a bearing surface and a fastener member. A space is defined between the outer cap and the inner cap. A compact vaporized fuel adsorption canister (hereinafter, “canister”) is provided in the space, and the canister adsorbs a vaporized fuel.
However, there is a limit to the space between the outer cap and the inner cap in terms of size. Due to this, it is disadvantageously quite difficult to obtain a canister appropriately performing inflow of the vaporized fuel, adsorption of the vaporized fuel, and smooth outflow of gas after the adsorption. It is particularly required to smoothly flow out the gas from which the vaporized fuel has been adsorbed from the canister. However, the outer cap closes an outlet of the canister, which makes it disadvantageously difficult to smoothly flow out the gas from the outlet. If the outlet is closed, the internal pressure of the fuel tank disadvantageously rises.
The space between the outer cap and the inner cap has a limited height and is, therefore, flat in shape. If the canister is accommodated in the space, a housing serving as an outer envelope of the canister is forced to be flat according to the shape of the flat space. In this case, the vaporized fuel flowing into the housing circulates through only limited channels, which makes it disadvantageously difficult to uniformly use the adsorbent filled up in the housing and to thereby adsorb the vaporized fuel.